I am not aware of any in-depth Siemens documentation regarding compiled/interpreted differencesfor 300 vs. 400. All I know at this time is that when you download a program in 300 the cod gets "compiled" so each MC7 instruction is converted to equivalent μC code and executed.In 400 the MC7 code is downloaded as it is, the STEP7 ASIC takes each opcode and executes. I don't think this is the same as Java or VB executes the opcodes in interpreted mode.Bottom line I think is not very important where/how you STEP7 program is executed, it's suppose to be transparent whether is interpreted or compiled. There are some minor differences between the two modesespecially regarding /FC status bit (in 300 is known in compile time where in 400is calculated inRT).

A S7-400 have also more communication resources, so that when you have a lot of communication it is better to use a S7-400. When you use a CP {Communication Processor} then the CPU stays the bottleneck, the CPU gives the amount of communication. [;)]

I hope that the answer will help, if you have still questions, don't hesitate to ask me.

All the best, LateNever say never, think in solutions, not in trouble......